Lipid metabolism Flashcards
Which of the following statements regarding beta-oxidation is FALSE?
A. It is the most important pathway for oxidation of fatty acids.
B. NADP serves as the oxidizing agent.
C. The end product of this process is acetylCoA.
D. The process occurs in the mitochondria.
B
What is the net ATP produced through beta oxidation from a 12-carbon saturated fatty acid?
A. 78
B. 80
C. 98
D. 108
A
The synthesis of fatty acids in our bodies requires the initial
carboxylation of acetyl CoA by acetyl CoA carboxylase. Which of the following is a source of acetyl CoA for this purpose?
A. Oxidative decarboxylation of pyruvate from glucose
B. Oxidative degradation of some proteins
C. Beta-oxidation of long-chain fatty acids
D. All of the above
D
Which of the following sources contributes the greatest to the cholesterol levels in the body?
A. Dietary sources
B. De novo synthesis in the liver
C. Extrahepatic tissues
D. Lipoprotein catabolism
B
What is a major point of regulation for the synthesis of cholesterol?
A. HMG - CoA Synthase
B. HMG - CoA Reductase
C. HMG- CoA Lyase
B
A high carbohydrate diet is associated with elevated triglycerides in blood. This is because glycerol is produced from the breakdown intermediate of glucose hydrolysis. Which intermediate is converted to glycerol?
A. Fructose-1,6-biphosphate
B. G3P
C. Dihydroxyacetone phosphate
D. Pyruvate
C
Which of the following is a derivative of cholesterol?
A. Hormones
B. Bile salts
C. Vitamin D
D. AOTA
D
Which of the following apoproteins serves as an inhibitor of the lipoprotein lipase (LPL)?
A. Apoprotein A-I
B. Apoprotein C-I
C. Apoprotien C-II
D. Apoprotein C-III
D
Fatty acids need certain substrates to facilitate transport through the intracellular compartments to generate energy in the form of ATP. What substrate is necessary for the entry of fatty acids from the intermitochondrial space to the mitochondrial matrix?
A. Co-enzyme A
B. Carnitine
C. Citrate
D. Co-enzyme Q
B
Which of the following processes involved in beta-oxidation splits off 2-carbon units from the carboxy-end of the fatty acids?
A. Dehydrogenation
B. Hydration
C. Oxidation
D. Thiolysis
D
During periods of starvation, our body mobilizes the fats in our body for energy production and glucose formation. What is the only substrate in fatty acid metabolism that is capable of being converted to glucose?
A. Acetyl CoA
B. FADH2
C. NADH
D. Propionyl CoA
A
What substrate in the citric acid cycle serves as the entry point for the glucogenic (glucose formation) transformation of fats?
A. Isocitrate
B. α-Ketoglutarate
C. Succinate
D. Malate
C
Which of the following statements regarding the control of fatty acid oxidation is FALSE?
A. Hormones control the availability of fatty acid substrates for oxidation.
B. Epinephrine regulates triacylglycerol lipase by controlling the cAMP regulatory cascades.
C. Glucagon leads to the consumption of fatty acids.
D. Malonyl-CoA controls uptake of fatty acyl-CoAs by inhibiting carnitine acyltransferase I.
C
Which of the following statements regarding fatty acid synthesis is TRUE?
A. The process mainly occurs in the adipose tissue.
B. It occurs whenever there is a caloric deficiency in the diet.
C. The major source of carbon is dietary carbohydrates.
D. The main pathway occurs in the mitochondria.
C
Acetyl CoA carboxylase catalyzes the rate-limiting step of fatty acid synthesis. What is the product of this step?
A. Acetyl CoA
B. Propionyl CoA
C. Malonyl CoA
D. Palmitoyl CoA
C
Which of the following statements is/are TRUEregarding the process of elongation of a fatty acid?
A. Elongation occurs in the endoplasmic reticulum
B. The process uses NADPH as reductant
C. Malonyl CoA lengthens the fatty acid by donating 2 carbons
D. All of the above
D
Omega 3 fatty acids have become a craze for good health. Several commercial products claim to contain these so-called “beneficial fats”. Which of the following is true regarding these fatty acids?
A. They can be synthesized by the human body de novo.
B. They are found only in deep sea fishes and not in plants.
C. They can be synthesized in the human body only when the initial substrates are acquired from the diet.
D. The initial substrate which must be obtained in the diet is oleic acid.
c
Which of the following statements BEST describes fats in caloric homeostasis?
A. Fats compose the least amount in our diet but the most of our energy stores
B. Fats produce more energy because they are hydrophobic.
C. Fats pass easily through the cell membrane and are easily transported.
D. Fat stores in our bodies are almost entirely derived from ketogenic amino acids.
A
Which of the following BEST describes fatty acid stores?
A. Fats comprise the smallest part in our diet so that our body stores very little of it.
B. Deamination of ketogenic amino acids is a major source of fatty acid stores.
C. Serum free fatty acid levels are highest in starvation due to mobilization of triglycerides.
D. Another reason very little fatty acids are stored is their large molecular weight.
C
Which of the following about ketogenesis is false?
a. It occurs in the liver exclusively
b. It occurs in the mitochondria
c. It uses carbon atoms from acetyl CoA
d. Both acetoacetic acid and beta-hydroxybutyrate are weak acids
D
Odd-numbered fatty acids can enter the glucogenic pathway through proprionyl CoA, which can form what intermediate of the Krebs cycle?
a. Citrate
b. Alpha-ketoglutarate
c. Succinyl CoA
d. Malate
C
Acyl-CoA dehydrogenase, the enzyme that catalyzes the first step of beta-oxidation, has three isozymes specific fot a range of fatty-acyl chain lengths. What are they?
VLCAD for 12-18 carbon
MCAD for 4-14 carbon
SCAD for 4-8 carbons
What is the electron acceptor in the first reaction of beta-oxidation?
FAD
Products of the β-oxidation of a 16-carbon chain saturated fatty acid
7 FADH2, 7 NADH, 7 acetyl-CoA
Total ATP yield of the complete breakdown of a 16-carbon chain saturated fatty acid
106 ATP
Products of the β-oxidation of a 18-carbon chain monousaturated fatty acid
9 FADH2, 9 NADH, 9 acetyl-CoA
Products of the β-oxidation of a 18-carbon chain saturated fatty acid
8 FADH2, 8 NADH, 8 acetyl-CoA
Why does the β-oxidation of unsaturated fa require additional reactions to the β-oxidation of saturated fa?
The enzyme enoyl-CoA hydratase only acts on trans double bonds. Unsaturated fats that occur in nature have cis double bonds, thus requiring additional steps wherein another enzyme converts the cis double bonds to trans so that enoyl-CoA hydratase would be able to act on it.
When are fatty acyl groups committed to oxidation to acetyl-CoA?
When they enter the mitochondrion
Which enzymes regulate fa catabolism?
Carnitine acyltransferase I, β-hydroxyacyl-CoA dehydrogenase, thiolase/ acyl-CoA acyltransferase
How is carnitine acyltransferase I regulated?
It is allosterically inhibited by malonyl-CoA
How is β-hydroxyacyl-CoA dehydrogenase regulated?
It is inhibited by its product, NADH
How is thiolase regulated?
It is inhibited by it’s product, acetyl-CoA
What is the main difference between β-oxidation of even numbered carbon chains and odd numbered carbon chains?
β-oxidation of even chains produce acetyl-CoA as final product of the last carbons. β-oxidation of odd chains produce proprionyl-CoA as final product of the last carbons.
Which molecules are ketone bodies?
Acetone, acetoacetate, and D-β-hydroxybutyrate
Which tissues cannot use ketone bodies as fuel?
Liver
Where are ketone bodies formed?
Hepatocytes
What is the importance of the production and export of ketone bodies to the maintenance of acetyl-CoA levels in the liver?
The liver contains only a limited amount of coenzyme A, and when most of it is tied up in acetyl-CoA, β-oxidation slows for want of free CoA. The production and export of ketone bodies frees CoA, allowing continued fa oxidation.
What is acidosis?
The condition when increased blood levels of acetoacetate and D-β–hydroxybutyrate lower the blood pH
What is ketosis?
The condition when ketone bodies in the blood and urine of individuals reach extraordinary levels
9- mg/100mL blood concentration (normal: < 125 mg/24hr)
Which of the following is not a ketone body?
A. acetone
B. B-hydroxybuterase
C. acetoacetate
D. α-hydroxybuterase
D
FA synthesis enzyme?
A. acetyl CoA synthetase
B. F. acid synthase
C. propionyl coA carboxylase
D. B ketoacyl synthetase
B
B oxidation occurs in the
A. cytoplasm
B. mitochondria
C. smooth ER
B
TAG synthesis?
A. mitochondrion
B. ER
C. cytosol
C
After the FFA and monoacylglycreols have been absorbed in the intestinal epithelium, they need to be re-esterified inside the enterocyte to produce TAG. Which of the following enzymes is responsible for making this process possible?
A. DGAT
B. ACAT
C. Lipoprotein
D. LCAT
A
Which of the ff statements about lipid synthesis is INCORRECT?
a.Glucose provides the reducing
b. It occurs in the cytoplasm
c. Two carbons are added from acetylCoA
d. Oleic acid is the first fatty acid equivalents
successivelyq
D
Malonyl-CoA is formed from which precursor?
Acetyl-CoA
Enzyme that converts acetyl-CoA to malonyl-CoA
Acetyl-CoA carboxylase
Fatty acid synthase I of mammals have how many active sites?
Seven
Fatty acid synthesis in fatty acid synthase I leads to a single product, and has how many intermediates released?
No intermediates are released
FA synthesis occur in which part of the cell?
Cytosol
Acetyl-CoA from the oxidation of fatty acid is the most significant source of acetyl-CoA for fa synthesis. T/F
F
It is not a significant source for fa biosynthesis in animals because the two pathways are reciprocally regulated
Acetyl-CoA used for biosynthesis is from which part of the cell?
Mitochondrial matrix
To what molecule is acetyl-CoA transformed to transport it out of the mitochondria?
Citrate
With which molecules does acetyl-CoA combine to form citrate?
Oxaloacetate
Enzyme that forms citrate from acetyl-CoA and oxaloacetate
Citrate synthase
Enzyme that regenerates acetyl-CoA and oxaloacetate after exit the mitochondria
Citrate lyase
Why does acetyl-CoA have to be converted to citrate?
Because the mitochondrion has no acetyl-CoA transporters
After citrate is cleaved back to oxaloacetate and acetyl-CoA in the cytosol, what becomes of oxaloacetate?
It is converted to malate in order to be transported back into the mitochondria
Which transporter does malate use to get inside the mitochondria?
Malate-α-ketoglutarate transporter
Most malate produced in the cytosol is used for what?
Generation of cytosolic NADPH
Which enzyme catalyzes the reaction that uses malate to produce NADPH?
Malic enzyme
The products of the reaction catalyzed by malic enzyme
NADPH and pyruvate
How is the activity of acetyl-CoA carboxylase regulated?
It is inhibited by palmitoyl-CoA and phosphorylation and allosterically activated by citrate
Which hormone activates citrate lyase?
Insulin
Which hormone deactivates acetyl carboxylase?
Glucagon and epinephrine
What is the principal product of fatty acid synthase system i animal cells?
Palmitate
When the 16-carbon chain of palmitoly-CoA is elongated by two carbons, what molecule is formed?
Stearoyl-CoA
TAG and which other molecule are synthesized from the same precursor?
Glycerophospholipids
Which is the last common precursor of TAG and glycerophospholipids?
Phosphatidic acid
